Hydraulic fracturing (or “fracking”) is a well-known process utilized by the oil and gas industry to create and enlarge fractures in underground shale formations. The fractures allow oil and natural gas to move more freely through the shale formations and ultimately flow to the surface. In the fracking process, explosions are set off to create the fractures and then high-pressure fluid is injected into the well in order to perpetuate the fracturing and hold the fractures open.
The fracturing fluid is typically comprised of water containing a proppant and chemical solution mixed therein. The fracturing fluid is often composed of between about 98-99.5% water and sand with the additional chemical solution accounting for about 0.5-2%. The water includes, in significant part, freshwater that must be transported to the well site by tanker truck or piping. The proppant, which is often sand or a similar material, is used to keep the fractures from closing after the injection has stopped. The chemical solution includes a variety of additives having dosage rates that vary with the location and condition of the specific well. These additives may include, but are not limited to, acids (e.g., hydrochloric acid), corrosion inhibitors (e.g., alcohols, organic acids, polymers, sodium salt, glycol and amide), iron control chemicals (e.g., sodium compounds and citric acid), antibacterial agents, biocides (e.g., gluteraldhyde, alcohols, sodium salt, sodium hydroxide and bromide salt), scale inhibitors (e.g., alcohols, organic acids, polymers, sodium salt, glycol and amide), friction reducers (e.g., polymers, hydrocarbons and water soluble polymers), surfactants (e.g., alcohols, glycols and hydrocarbons), gelling agents (e.g., guar gum, hydrocarbons and polymers), breakers (e.g., ammonium persulfate, sodium and potassium salts) and crosslinkers (e.g., polyol and borax).
The fracking process typically requires between about one million and five million gallons of water or more per well. A portion of the water that is injected into the well returns to the surface as “flowback water.” While the flowback water returns to the surface over a period of three to four weeks, most of the flowback water returns within the first seven to ten days. The volume of recovery is generally between about 20-60% of the volume that was initially injected into the well. The rest of the fluid is absorbed in the shale formation. At a certain point, there is a transition from primarily recovering flowback water to primarily recovering “produced water,” which is water naturally occurring in the shale formation that flows to the surface over the life of the well.
Upon returning to the surface and exiting the well, the flowback water and produced water is generally collected in tanks, open pools or lagoons located near the well. From there, the flowback water and produced water is pumped into tanker trucks and transported from the well site to a deep disposal well where the water is placed back into the ground. Each disposal well typically costs several million dollars to drill and maintain. Disposal wells can additionally create environmental and water source contamination concerns.
The flowback water and produced water is typically contaminated with man-made and naturally-occurring substances. The water is contaminated with the spent chemicals that are mixed into the fracking water prior to its injection into the well, as discussed above. The water is also contaminated with naturally-occurring substances residing below the Earth's surface. For example, the water may have elevated levels of Kjeldahl nitrogen, petroleum residue, sodium, ammonia, chloride, sulfate, chloride sulfate, total dissolved solids (TDS), chloride, barium, strontium, boron, benzene, ethylbenzene, toluene, xylene, glycols, 2-butoxyethanol, radionuclides such as radium isotopes (e.g., radium-226 and radium-228), uranium-238 and lead-210 and other naturally occurring radioactive material (“NORM”) found in the shale formations. Additionally, some scientists believe that the explosions occurring during the fracturing of the shale formation set off chain reactions that result in the creation of radioactive material in addition to the NORM already present in the shale formations.
In order for the flowback water and the produced water to be reused as fracturing water or discharged to the environment, it must first be treated. As such, a need exists for a system and method for treating contaminated flowback water and produced water such that it can be reused and the cost and environmental concerns resulting from the disposal wells can be eliminated. A particular need exists for a system and method for removing radioactive materials from flowback water and produced water. A further need exists for a system that is self-contained and is mobile between well sites and may be scaled up or down depending upon the amount and quality of the water to be treated.